Tag Archives: molecule

One of my favorite chemical reactions is frequently called “Elephant’s Toothpaste.” It creates a LOT of gas from very little liquid, which makes an impresive show, and the main ingredient, hydrogen peroxide, is already familiar to most people.

Here is series of photos of the Elephant’s Toothpaste reaction (sometimes very fun and very messy go together):

If you ask someone what they use hydrogen peroxide for, they’ll usually tell you it can clean minor cuts and scrapes or that it’s good for household cleaning.

When you pour hydrogen peroxide on a cut, what do you notice? The first thing you’ll notice is that it stings a bit, but you’ll also see bubbles at the site of the cut. The bubbles are evidence that there is a chemical reaction; you started with one substance and ended up with something completely different (there was no gas before you poured the peroxide on the cut, and there were gas bubbles after, so the gas is new).

The formula H2O is almost universally understood as another name for water; this chemical formula indicates two hydrogen atoms stuck onto every oxygen atom. Hydrogen peroxide’s chemical formula is H2O2, so you can think about it as water with extra oxygen attached. When you pour it on your cut, the hydrogen peroxide decomposes into liquid water (H2O) and oxygen gas (O2). The bubbles you see are oxygen bubbles.

In case you were wondering, oxygen atoms don’t like to hang around alone, so they bond to each other and that’s why we get O2 instead of just O. If you are a person who counts atoms and you noticed that our atoms didn’t quite add up, you’re right; the balanced equation for the reaction is usually written:

2H2O2 –> 2H2O + O2

The large 2’s mean two of that whole atom (two hydrogen peroxide molecules can react to create two water molecules and one oxygen molecule). If the equation looks strange to you, don’t worry; just know that the molecules do the right thing.

What isn’t included in this equation is that the blood in your cut initiates this reaction (it contains an enzyme called catalase).

Something to try:

If you have a bottle of 3% hydrogen peroxide at home, I have a project for you (if you are a kid, do this with your parents).

You need 3% hydrogen peroxide, yeast, dish soap, and a cup or bowl. Most people face bigger hazards in the kitchen every time they cook, but it is a good idea to wear safety glasses or goggles just in case something splashes or falls and breaks, and hydrogen peroxide in your eye would definitely sting.

Put some yeast (I used about a teaspoon of quick-rise yeast) in the bottom of your container:

Add enough water to wet the yeast and swirl it around or stir it a little:

Now add a little dish soap and swirl or mix again:

You may want to set the container or a plate to help contain the mess before you add the hydrogen peroxide (I added approximately 1/4 cup (60 mL):

Here the hydrogen peroxide is starting to react and the soap catches the oxygen gas and it starts to produce foam.

But it keeps going:

And going:

And going:

And going:

The yeast contains catalase (your blood does too), and that helps the reaction happen faster, but the big thing to notice is that a small volume of hydrogen peroxide reacted to create a big volume of oxygen gas (the soap just helped catch it so we could see it better). Any time you start with a liquid and make a gas, if the gas can expand, it will, and usually a lot.

Oh, and even though the reaction is called Elephant’s Toothpaste, please don’t try to eat it. Yuck!

All you really need to know (for now) is that the chemical elements are pure substances usually considered the building blocks of all the matter in the universe. Hydrogen, oxygen, carbon, lithium, potassium, bismuth, neon, helium, tungsten, copper, and gold are all elements, along with about a hundred or so others. Tom Lehrer wrote a fantastic and ridiculous song, The Elements, which names them all (or at least all the ones known when he wrote the song).

Most of the time we encounter the elements as compounds (like a water molecule is two hydrogen atoms attached to one oxygen atom) or mixtures (like air) or alloys (a special kind of mixture) like steel (iron and friends) or brass (copper and zinc).

So, returning to just the elements, each element has unique characteristics, just like peanut butter is different from jelly. Each element has a certain number of protons (the atomic number), and an atomic mass (essentially how much stuff there is in an average atom of that element), and a number of valence electrons (which determines a lot about how the element reacts).

Don’t get bogged down in what each of those things means, just remember that different elements have different characteristics, just like some shapes have curves and others have angles, or like some animals have two legs, some four, some more, and some none.

Anyway, the point is that if you have different characteristics, you can do some sorting, and sorted options are easier to deal with than a pile of randomness (I bet you select a sorted pair of matching socks most of the time, and prefer that your oatmeal isn’t stored in the same container with chocolate chips, soy sauce, and croutons in your pantry).

Science LOVES classification and sorting, and there are all sorts of systems and methods to do it. One word for these systems is taxonomy (to be distinguished from taxidermy, though you may certainly classify and sort your stuffed road-kill should you so choose.) Taxonomy often refers to sorting and classifying living or once living things, but it can also mean classifying rocks, stars, etc., based on their characteristics.

Things to Try:

Periodic Table of Office Supplies?

Instead of sorting elements or classifying animals into classes or species, I sorted some office supplies of the order Paperclippius, more commonly known as paper clips. Go ahead and try this with your own office supplies, pocket change, or whatever small items are handy.

Here is an assortment of specialty paperclips — how could you sort these?

You might sort by color:

Or by shape:

And both ways have value. If we sort by color and shape at the same time, a ‘table’ starts to form:

And the next step……

And the next step……

And then we might complete the table this way:

But we could have set up our sorting table like this:

Or like this:

And those ways are just as good — they all sort by both attributes (shape and color), and we know where each type of clip ‘belongs’ in the table. If we had everything laid out except the blue triangle clip, you would notice the ‘hole’ and know approximately what that clip should look like.

The existence of many elements in the periodic table was correctly predicted before those elements were discovered, because of the ‘holes’ left in the early versions of the table. Pretty cool, right?